Heretofore, water washed paint spray booths have utilized sludge recovery systems to separate the spent paint material picked up by the water as it passed through the booth. In one type system, the water carrying the spent paint is allowed to drop or flow out of the booth into a recovery tank or pit. In the tank or pit, the water is treated with chemicals, such as flotation chemicals which assists the spent paint material to separate or segregate, and, in this instance, float to the top. After sufficient time for the separating or flotation action to occur, the spent paint material floats to the top and is allowed to flow over a weir into a separation area wherein it can be concentrated. From there, the concentration spent paint material is drawn off to a centrifuge which separates the spent paint from the remaining water, and the remaining water is sent back and is reused in booth.
During the operation of the booth, and even during downtime, water in the booth system tends to be reduced in quantity, either due to evaporation, water being blown out the booth eliminator section (the booth having a motor driven fan to usually exhaust air, including some water out of the booth) and just variations in operating conditions. The latter could be due to a single pit or tank serving more than one booth and one or more booths operating conditions being changed or shut down. Changes in both water quantity and consequently the water level and the sludge recovery can have adverse consequences, particularly on the operations of sludge systems using weirs. For example, changes of water level effects the water crests flowing over the weirs and their operation. Too large a water crest can cause excess water to be supplied to the separator making it more difficult to extract the sludge efficiently. Too little water in the crests, on the other hand, can cause hang ups of the sludge, and partial or complete blockages, and also reduces the efficiency of the operation. Keeping a constant water level in the tank is important as it helps keep weirs operating consistently. Heretofore, one attempt to do so was to try to use a float controlling the make up water valve in the large pit in which the chemical action or flotation action takes place. While this system worked, it was slow to react to changes and allowed considerable variation in water level in other portions of the system. Due to the difficulty in controlling the water level in such way, it was difficult to get consistent efficient operation of a system based on paint sludge flotation and some times other systems were used such as sinking or suspension, that is, causing the spent paint to first sink, be drawn off the bottom or to be kept in suspension and just drawn off. Prior to the present invention, there was not a reliable way to maintain water level efficiently and permit the use of spent paint flotation and weirs.